Forest hammock of slash pine and saw palmetto, Everglades National Park, Florida (© Mary Liz Austin/Alamy)

Arbor Day celebrates the quiet power of trees—the way they steady ecosystems, shelter wildlife, cool cities, and shape the environments we rely on every day. Observed in the United States on the last Friday in April, the day encourages communities here—and in many other countries, where dates vary according to growing season—to plant, protect, and care for forests of every kind, from neighborhood canopies to iconic wildlands.